1. Field of the Invention
The present invention relates to a storage medium storing a game program for displaying on a screen of a display device a virtual image obtained when at least one object existing in a virtual space is observed from a predetermined point of view in the virtual space, and a game apparatus.
2. Description of the Background Art
In recent years, as the performance of computers included in game systems is increased, three-dimensional games employing three-dimensional computer graphics technology are becoming popular. In the three-dimensional game, an object composed of polygons, such as a character object, a building object or the like, is provided in a three-dimensional game space, and what is seen from a predetermined point of view in the game space is displayed as a three-dimensional game screen. In most cases, the predetermined point of view is directed to a player character object (hereinafter simply referred to as a player character) so as to cause a player to recognize the player character which is operated by the player. In this case, since the predetermined point of view is moved while keeping a predetermined positional relationship with the player character, an obstacle may get in the way of line of sight on which the player character is observed. Therefore, there is a disclosed technique of causing the obstacle to become transparent or translucent in such a case.
For example, there is a disclosed image generating apparatus (e.g., Japanese Laid-Open Patent Publication No. 9-50541) in which it is determined whether or not an obstacle conceals a player character as viewed from the predetermined point of view, and when it is determined that the obstacle conceals the player character, a process of causing the obstacle to become transparent is performed. Also, there is a disclosed game apparatus (e.g., Japanese Laid-Open Patent Publication No. 9-299613) in which, when a player character is concealed by a wall or a floor in a game space, the wall or floor is caused to become transparent. Also, there is a game apparatus (e.g., Japanese Laid-Open Patent Publication No. 2002-197486) in which a game space is divided into a plurality of regions, depending on a distance in a depth direction from the predetermined point of view, an opacity is set for each divided region, and translucency synthesis is performed with respect to each pixel included in each region using the opacity. Also, there is a disclosed game apparatus (e.g., Japanese Laid-Open Patent Publication No. 11-42370) in which a transparency of each pixel is set, depending on a distance from the predetermined point of view to each pixel (dot) unit of each object.
However, the apparatuses as disclosed in the above-described documents conventionally have the following problems. In the apparatuses disclosed in Japanese Laid-Open Patent Publication Nos. 9-50541 and 9-299613 described above, when a player character gets concealed by an obstacle, the obstacle is caused to instantaneously become transparent. Therefore, since the obstacle so far seen suddenly disappears, the player feels awkward or unnatural. In the game apparatuses disclosed in Japanese Laid-Open Patent Publication Nos. 2002-197486 and 11-42370, since the transparency is changed depending on the distance from the predetermined point of view, the transparency is gradually changed as long as the obstacle gradually moves closer or away, thereby making it possible to significantly reduce the sense of awkwardness or unnaturalness which the player feels. However, for example, when an obstacle suddenly appears on a screen (before the player's eyes) upon switching of screens, the obstacle is caused to instantaneously become transparent (or translucent). Therefore, the obstacle appears for a moment and immediately disappears, which causes the player to feel awkward or unnatural.